The present invention relates to quadratic acid or squaric acid, see JACS 84, 2920 (1962), amide derivatives which are effective stabilizers for synthetic resins, and to synthetic resin compositions containing these stabilizers.
It is known that synthetic resins, under the effects of light and heat as well as under the influence of natural weathering, tend to yellow, to become brittle, and finally to disintegrate entirely. The resultant damage can reach considerable proportions. Therefore, it has been customary for some time to add a number of stabilizers to synthetic resins exposed to particularly deleterious environmental influences.
These stabilizers are compounds which have quite diverse chemical structures and which stabilize the synthetic resins against the effects of the natural environment by various mechanisms whose details are unknown in many cases. DOS 2,606,026 and DOS 2,634,957 disclose 1-oxa-4,8-diazaspiro[4,5]decanes which are added to polymers along with other customary stabilizers. The commercially available stabilizer designated TINUVIN 770 (see Comparative Example A) does not fulfill expectations with respect to its light-stabilizing effect.
The light-stabilizing effect of tetramethylpiperidine and its derivatives is due to their ability to efficiently scavenge radical intermediates formed in photooxidation processes, as disclosed in J. Polym. Sci. Polym. Chem. Ed., 19, 807 (1981).
DOS 2,638,855 discloses a quadratic acid amide substituted by a tetramethylpiperidine ring. The quadratic acid 1,3-bis-2',2',6',6'-tetramethylpiperidon-(4')-ide described therein not only differs structurally from the derivatives described herein, but furthermore, no commercially feasible syntheses for this compound are known. Certain quadratic acid 1,3-bisamides provided to be effective stabilizers in weathering tests due to their absorbing and quenching effects, as disclosed, e.g., in DOS 2,638,855.
However, all of the conventional stabilizers or stabilizer combinations have deficiencies which are especially evident in thin synthetic resin layers, viz.:
1. They are too volatile. PA1 2. They can be easily extracted. PA1 3. They exhibit a considerable tendency to migrate. PA1 wherein m is an integer of 2-6; n is 0 or 1, PA1 R.sub.3 is H, CH.sub.3, CH.sub.2 --CH.sub.2 --OH, CH.sub.2 --COOH or CH.sub.2 --CH.sub.2 --COOH; PA1 0.ltoreq.p.ltoreq.2.
A need therefore continues to exist for stabilizers which do not show these disadvantages.